1. Field of the Invention
The present invention relates to an optical multiplexer/demultiplexer and an optical multiplexer/demultiplexer apparatus.
2. Discussion of the Background
Recent dramatic increase in internet traffic requires an increase in transmission network capacity. One of the solutions for this requirement is wavelength division multiplexing (WDM) technology. In the wavelength division multiplexing technology, a plurality of lights having wavelengths different from each other are multiplexed and are transmitted in one optical fiber. Accordingly, the transmission capacity may increases by the number of lights multiplexed.
In order to realize the wavelength division multiplexing system, optical device such as optical multiplexers/demultiplexers are required.
The optical multiplexer/demultiplexer multiplexes lights having wavelengths different from each other or demultiplexes a light to lights having different wavelengths. For example, a multiplexed light multiplexed by an optical multiplexer/demultiplexer is transmitted to an optical fiber. Further, the multiplexed light transmitted in the optical fiber is demultiplexed by an optical multiplexer/demultiplexer and lights having different wavelengths are output.
Such optical multiplexer/demultiplexer is, for example, an arrayed waveguide grating (AWG), a Mach-Zehnder interferometer and the like.
Conventionally, the Mach-Zehnder Interferometer type optical multiplexer/demultiplexer may multiplex lights or demultiplex a light which has close wavelengths, for example, 1549 nm and 1551 nm.
According to one aspect of the present invention, an optical multiplexer/demultiplexer includes a first optical waveguide, a second optical waveguide, a first directional coupling portion in which the first and the second optical waveguides are provided to transfer a light between the first and second optical waveguides, and a second directional coupling portion in which the first and the second optical waveguides are provided to transfer a light between the first and second optical waveguides. The first and second directional coupling portions are provided such that a length of the first optical waveguide between the first and second directional coupling portions and a length of the second optical waveguide between the first and second directional coupling portion have a difference (xcex94L). A product (nxc3x97xcex94L) between the difference (xcex94L) and a refractive index (n) of the first and second optical waveguides approximates a product between a cross-propagation wavelength (xcex2) and a value (Nxe2x80x2) substantially equal to an integer (N), and a product between a through-propagation wavelength (xcex1) and the value (Nxe2x80x2)xc2x10.5. The cross-propagation wavelength (xcex2) is a wavelength of a cross-propagation light which propagates from the first optical waveguide to the second optical waveguide or from the second optical waveguide to the first optical waveguide. The through-propagation wavelength (xcex1) is a wavelength of a through-propagation light which propagates from an input to an output of the first optical waveguide or from an input to an output of the second optical waveguide. Power coupling ratio differences between first power coupling ratios of the first and second directional coupling portions with respect to the cross-propagation wavelength (xcex2) and second power coupling ratios of the first and second directional coupling portions with respect to the through-propagation wavelength (xcex1) are at least approximately 1% and at most approximately 10%. Third power coupling ratios of the first and second directional coupling portions with respect to an average wavelength of the cross-propagation wavelength (xcex2) and the through-propagation wavelength (xcex1) are at least approximately 45% and at most approximately 55%.
According to another aspect of the present invention, an optical multiplexer/demultiplexer includes a first optical waveguide, a second optical waveguide, a first multi-mode interferometer waveguide to which the first and second optical waveguides are connected, and a second multi-mode interferometer waveguide to which the first and second optical waveguides are connected. The first and second multi-mode interferometer waveguides are provided such that a length of the first optical waveguide between the first and second multi-mode interferometer waveguides and a length of the second optical waveguide between the first and second multi-mode interferometer waveguides have a difference (xcex94L). A product (nxc3x97xcex94L) between the difference (xcex94L) and a refractive index (n) of the first and second optical waveguides approximates a product between a cross-propagation wavelength (xcex2) and a value (Nxe2x80x2) substantially equal to an integer (N), and a product between a through-propagation wavelength (xcex1) and the value (Nxe2x80x2)xc2x10.5. The cross-propagation wavelength (xcex2) is a wavelength of a cross-propagation light which propagates from the first optical waveguide to the second optical waveguide or from the second optical waveguide to the first optical waveguide. The through-propagation wavelength (xcex1) is a wavelength of a through-propagation light which propagates from an input to an output of the first optical waveguide or from an input to an output of the second optical waveguide. Power coupling ratio differences between first power coupling ratios of the first and second multi-mode interferometer waveguides with respect to the cross-propagation wavelength (xcex2) and second power coupling ratios of the first and second multi-mode interferometer waveguides with respect to the through-propagation wavelength (xcex1) are at least approximately 1% and at most approximately 10%. Third power coupling ratios of the first and second multi-mode interferometer waveguides with respect to an average wavelength of the cross-propagation wavelength (xcex2) and the through-propagation wavelength (xcex1) are at least approximately 45% and at most approximately 55%.
According to yet another aspect of the present invention, an optical multiplexer/demultiplexer apparatus includes a plurality of optical multiplexers/demultiplexers provided to repeat multiplexing or demultiplexing. Each of the optical multiplexers/demultiplexers includes a first optical waveguide, a second optical waveguide, a first directional coupling portion in which the first and the second optical waveguides are provided to transfer a light between the first and second optical waveguides, and a second directional coupling portion in which the first and the second optical waveguides are provided to transfer a light between the first and second optical waveguides. The first and second directional coupling portions are provided such that a length of the first optical waveguide between the first and second directional coupling portions and a length of the second optical waveguide between the first and second directional coupling portion have a difference (xcex94L). A product (nxc3x97xcex94L) between the difference (xcex94L) and a refractive index (n) of the first and second optical waveguides approximates a product between a cross-propagation wavelength (xcex2) and a value (Nxe2x80x2) substantially equal to an integer (N), and a product between a through-propagation wavelength (xcex1) and the value (Nxe2x80x2)xc2x10.5. The cross-propagation wavelength (xcex2) is a wavelength of a cross-propagation light which propagates from the first optical waveguide to the second optical waveguide or from the second optical waveguide to the first optical waveguide. The through-propagation wavelength (xcex1) is a wavelength of a through-propagation light which propagates from an input to an output of the first optical waveguide or from an input to an output of the second optical waveguide. Power coupling ratio differences between first power coupling ratios of the first and second directional coupling portions with respect to the cross-propagation wavelength (xcex2) and second power coupling ratios of the first and second directional coupling portions with respect to the through-propagation wavelength (xcex1) are at least approximately 1% and at most approximately 10%. Third power coupling ratios of the first and second directional coupling portions with respect to an average wavelength of the cross-propagation wavelength (xcex2) and the through-propagation wavelength (xcex1) are at least approximately 45% and at most approximately 55%.
According to yet another aspect of the present invention, an optical multiplexer/demultiplexer apparatus includes a plurality of optical multiplexers/demultiplexers provided to repeat multiplexing or demultiplexing. Each of the optical multiplexers/demultiplexers includes a first optical waveguide, a second optical waveguide, a first multi-mode interferometer waveguide to which the first and second optical waveguides are connected, and a second multi-mode interferometer waveguide to which the first and second optical waveguides are connected. The first and second multi-mode interferometer waveguides are provided such that a length of the first optical waveguide between the first and second multi-mode interferometer waveguides and a length of the second optical waveguide between the first and second multi-mode interferometer waveguides have a difference (xcex94L). A product (nxc3x97xcex94L) between the difference (xcex94L) and a refractive index (n) of the first and second optical waveguides approximates a product between a cross-propagation wavelength (xcex2) and a value (Nxe2x80x2) substantially equal to an integer (N), and a product between a through-propagation wavelength (xcex1) and the value (Nxe2x80x2)xc2x10.5. The cross-propagation wavelength (xcex2) is a wavelength of a cross-propagation light which propagates from the first optical waveguide to the second optical waveguide or from the second optical waveguide to the first optical waveguide. The through-propagation wavelength (xcex1) is a wavelength of a through-propagation light which propagates from an input to an output of the first optical waveguide or from an input to an output of the second optical waveguide. Power coupling ratio differences between first power coupling ratios of the first and second multi-mode interferometer waveguides with respect to the cross-propagation wavelength (xcex2) and second power coupling ratios of the first and second multi-mode interferometer waveguides with respect to the through-propagation wavelength (xcex1) are at least approximately 1% and at most approximately 10%. Third power coupling ratios of the first and second multi-mode interferometer waveguides with respect to an average wavelength of the cross-propagation wavelength (xcex2) and the through-propagation wavelength (xcex1) are at least approximately 45% and at most approximately 55%.
According to the other aspect of the present invention, an optical multiplexer/demultiplexer includes a first optical waveguide, a second optical waveguide, a directional coupling portion in which the first and the second optical waveguides are provided to transfer a light between the first and second optical waveguides, and a multi-mode interferometer waveguide to which the first and second optical waveguides are connected. The directional coupling portion and the multi-mode interferometer waveguide are provided such that a length of the first optical waveguide between the directional coupling portion and the multi-mode interferometer waveguide and a length of the second optical waveguide between the directional coupling portion and the multi-mode interferometer waveguide have a difference (xcex94L). A product (nxc3x97xcex94L) between the difference (xcex94L) and a refractive index (n) of the first and second optical waveguides approximates a product between a cross-propagation wavelength (xcex2) and a value (Nxe2x80x2) substantially equal to an integer (N), and a product between a through-propagation wavelength (xcex1) and the value (Nxe2x80x2)xc2x10.5. The cross-propagation wavelength (xcex2) is a wavelength of a cross-propagation light which propagates from the first optical waveguide to the second optical waveguide or from the second optical waveguide to the first optical waveguide. The through-propagation wavelength (xcex1) is a wavelength of a through-propagation light which propagates from an input to an output of the first optical waveguide or from an input to an output of the second optical waveguide. Power coupling ratio differences between first power coupling ratios of the directional coupling portion and the multi-mode interferometer waveguide with respect to the cross-propagation wavelength (xcex2) and second power coupling ratios of the directional coupling portion and the multi-mode interferometer waveguide with respect to the through-propagation wavelength (xcex1) are at least approximately 1% and at most approximately 10%. Third power coupling ratios of the directional coupling portion and the multi-mode interferometer waveguide with respect to an average wavelength of the cross-propagation wavelength (xcex2) and the through-propagation wavelength (xcex2) are at least approximately 45% and at most approximately 55%.